Merge pull request #723 from shirosaki/enigmail

Fix an error to display pgp message with Enigmail 1.5.1
Get correct uri of a message for security status

We always use uri argument if it is available.
The uri argument is not supported by recent Enigmail.
https://sourceforge.net/p/enigmail/bugs/139/
Verify a message with attached signature

This feature doesn't work with recent version of Enigmail.
I fixed it to work with latest Enigmail. It may not work with older
version of Enigmail.